1. FIELD OF THE INVENTION
The present invention relates to a heating module for a mixture-compressing combustion engine. The heating module is arranged between an induction pipe and a cylinder head of the combustion engine, the induction pipe, the heating module and the cylinder head delimiting at least one intake port in which at least one electrically heatable heating element is arranged. The heating element constitutes a component of the heating module, and the heating element is connectable with connecting terminals to an electric current source. The joining surfaces between the induction pipe, the heating module and the cylinder head are each sealed by at least one sealing device.
2. DESCRIPTION OF THE PRIOR ART
A heating module is shown in German patent DE 43 14 283 A1. The electrically heatable heating element in that patent has a tub-shaped cross-section transverse to the direction of flow and can be connected to a flange which is a component of the intake port. Viewed in the direction of flow, the flange has a comparatively large thickness in order to be able to surround a wire through which a heating medium flows. In addition to electrical heating, the heating elements can be heated by a medium already heated by the engine, for example by coolant. Therefore, already a few minutes after a cold start of the engine, electrical heating of the heating element can be switched off, and only the coolant, which is heated anyway, is used for further heating. In addition, the intermediate flange which accommodates the heating elements can be designed to be so broad that the mounting surfaces of the injection nozzles can be integrated into the flange.
European patent EP 0 343 652 A1 shows a flange in which the suspension mount of the heating elements on the flange is very massive. The heavy dimensional design of this suspension mount results in a restriction of the intake air, so that a considerable full-load charge loss and a resulting reduction in the maximum possible engine power follows. Furthermore, during circumflowing, the massive suspension mounts result in dead spaces through which the air-fuel mixture does not flow so that, particularly at low temperatures of the intake air, the heating element and the suspension mounts, considerable amounts of liquid fuel, viewed in the direction of flow, deposit behind the suspension mounts on the intake port wall, the heating elements and the suspension mounts. This phenomena causes the HC and CO emissions to worsen, primarily during dynamic travel operation. The use of a relatively thick flange and a thick, separately installed sealing device leads to nonuniformities in the port, especially in the case of intake ports in which the joining surfaces between the cylinder head and the induction pipe are not arranged perpendicular to the center line of the intake port, and this promotes intake throttling loss. Besides the design restrictions resulting from this, in addition the expenditure for design changes in the subsequent application of a heating flange to an existing engine concept increases.